1. Field of the Invention
This invention relates to solvent soluble, biodegradable polyesters, method of production, and use thereof. These products are useful as biodegradable shaped articles and as biodegradable coatings.
2. Description of the Related Art
The inadequate treatment of municipal solid waste which is being put in landfills and the increasing addition of nondegradable materials, including plastics, to municipal solid waste streams are combining to drastically reduce the number of landfills available and to increase the costs of municipal solid waste disposal. While recycling of reusable components of the waste stream is desirable in many instances, the costs of recycling and the infrastructure required to recycle materials is sometimes prohibitive. In addition, there are some products which do not easily fit into the framework of recycling. The composting of non-recyclable solid waste is a recognized and growing method to reduce solid waste volume for landfilling and/or making a useful product from the waste to improve the fertility of fields and gardens. One of the limitations to marketing such compost is the visible contamination by undegraded plastic, such as film or fiber fragments.
It is desired to provide components which are useful in disposable products and which are degraded into less contaminating forms under the conditions typically existing in waste composting processes.
Polyesters have been considered for biodegradable articles and enduses in the past. Biodegradable polyesters can be described as belonging to three general classes; aliphatic polyesters, aliphatic-aromatic polyesters, and sulfonated aliphatic-aromatic polyesters. Aliphatic polyesters are polyesters derived solely from aliphatic dicarboxylic acids. Aliphatic-aromatic polyesters are polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids. Sulfonated aliphatic-aromatic polyesters are polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids and, in addition, incorporate a sulfonated monomer, such as the salts of 5-sulfoisophthalic acid. Many of these prior materials do not provide desired biodegradability and/or solubility in common solvents.
U.S. Pat. No. 4,104,262, teaches water-dispersible polyester resins. The water-dispersibility of the polyester resins is due, at least in part, to the incorporation of moieties of an alkali metal-sulfo group and to the very low molecular weights of the polymers, e.g., between 300 and 3,000. The low molecular weight polyester resins would tend to give brittle, low toughness films and coatings.
U.S. Pat. No. 4,340,519, teach aqueous dispersions of polyester resins which contain 0.5 to 10 mole percent of an aromatic dicarboxylic acid having a metal sulfonate group. Many of the polyesters of this patent incorporate neopentyl glycol. Example A-1, contained within Table 2 of the patent, incorporates 16.7 mole percent of isophthalic acid within the aromatic dicarboxylic acid component. This example was found to be crystalline, based on the reported melting point of 116xc2x0 C., and is not expected to be soluble in polar solvent. Such solubility is often desired, e.g., to allow solvent casting of coatings and films.
Miller, in U.S. Pat. No. 4,394,442, teaches a subbing layer composed of an aqueous dispersion of certain copolyester resins which incorporate 0.1 to 10 mole percent aromatic sulfonated compounds. The patent exemplifies copolyester resins which incorporate 10 mole percent, (based on the total of dicarboxylic acids), of the sodium salt of 5-sulfoisophthalic acid in combination with 56.7 mole percent, (based on the total of diols), di(ethylene glycol). Such polyesters that are soluble in water are often undesired because they do not have the desired dimensional stability in the presence of water.
The above-mentioned polyesters of the art often suffer from poor solubility in polar solvent systems, low molecular weights, which could lead to brittle films, or high moisture sensitivity, which could lead to dimensional instability under varying moisture conditions. The present invention overcomes these shortcoming and provides solvent soluble, film forming copolyesters which have improved moisture insensitivity.
The present invention provides a copolyester having an inherent viscosity of equal to or greater than about 0.3 dL/g comprising:
(a) about 20 to about 60 mole percent based on the moles of aromatic dicarboxylic acid or ester, of one or more of isophthalic dicarboxylic acid or an alkyl diester thereof,
(b) about 40 to about 80 mole percent based on the moles of aromatic dicarboxylic acid or ester, of one or more of terephthalic acid, an alkyl diester thereof, 2,6-naphthalene dicarboxylic acid, or an alkyl diester thereof,
(c) about 10 to about 60 mole percent based on the moles of dicarboxylic acid or ester, of one or more aliphatic dicarboxylic acids or an alkyl diester thereof,
(d) about 0.1 to about 5 mole percent based on the moles of total dicarboxylic acid or ester, of one or more alkali or alkaline earth metal salts of 5-sulfoisophthalic dicarboxylic acid or an alkyl diester thereof,
(e) about 90 to 100 mole percent based on the moles of glycols, of one or more aliphatic glycols, and
(f) 0 to about 10 mole percent based on the total amount of glycols of one or more of di(ethylene glycol) and tri(ethylene glycol).
Further objects, features and advantages of the present invention will become apparent form the detailed description that follows.
One aspect of the present invention provides solvent soluble, biodegradable sulfonated aliphatic-aromatic copolyesters with IV equal to or greater than about 0.30 dL/g, such as above about 0.4 or above about 0.5 dL/g. The IV should preferably be sufficient to give non-brittle films, but not so high as to give undesired high solution viscosities.
The sulfonated aliphatic-aromatic copolyesters are preferably comprised of (A), (B) (C), (D), and (E):
(A) about 89.9 to about 35, preferably about 88 to about 46, more preferably about 84.5 to about 47, mole percent (based on the total moles of dicarboxylic acid) of an aromatic dicarboxylic acid component comprised of (i) and (ii):
(i) about 20 to about 60, preferably about 25 to about 50, more preferably about 30 to about 40, mole percent, (based on the total moles of aromatic dicarboxylic acid), of isophthalic dicarboxylic acid or a lower alkyl (C1-C6) diester derived therefrom, such as dimethylisophthalate, diethylisophthalate, and the like and
(ii) about 80 to about 40, preferably about 78 to about 50, more preferably about 75 to about 60 mole percent, (based on the total moles of aromatic dicarboxylic acid), of an aromatic dicarboxylic acid selected from terephthalic acid and 2,6-naphthalene dicarboxylic acid, and lower dialkyl (C1-C6) esters derived therefrom, such as dimethylterephthalate, diethylterephthalate, dimethyl-2,6-naphthalene dicarboxylate, diethyl-2,6-naphthalene dicarboxylate, and the like;
(B) about 10 to about 60, preferably about 12 to about 50, more preferably about 15 to about 50 mole percent (based on the total moles of dicarboxylic acid) of a linear aliphatic dicarboxylic acid component comprised of one or more aliphatic dicarboxylic acids, which generally has from 2 to 36 carbon atoms, such as oxalic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, dimer acid, or mixtures therefrom, and lower dialkyl diesters derived therefrom, such as dimethyl oxalate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutaratate, dimethyl azealate, and the like;
(C) about 0.1 to about 5, preferably about 0.1 to about 4, more preferably about 0.5 to about 3 mole percent (based on the total amount of dicarboxylic acid) of a sulfonate component comprised of one or more alkali or alkaline earth metal salts of 5-sulfoisophthalic acid and lower (C1-C6) alkyl diesters derived therefrom, such as alkali or alkaline metal salts of dimethyl-5-sulfoisophthalate, alkali or alkaline earth salts of diethyl-5-sulfoisophthalate, and the like;
(D) 100 to about 90, preferably 100 to about 92, more preferably 100 to about 95 mole percent (based on total glycol) of an aliphatic glycol component comprised of a linear aliphatic glycol, preferably having from 2 to 6 carbon atoms, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and mixtures thereof; and
(E) 0 to about 10, preferably 0 to about 7.5, more preferably 0 to about 5 mole percent (based on total glycol) of a glycol component selected from di(ethylene glycol) and tri(ethylene glycol).
The polymer contains one or more alkali or alkaline earth metal salts of 5-sulfoisophthalic acid or an alkyl diester thereof. The amount of sulfo groups in the polymer should be about 0.1 to 5 mole percent. The alkali metal ion is, for example, sodium, potassium, or lithium. Alkaline earth metals such as magnesium are also useful. It has been found that as little as 0.1 mole percent of the sulfo group contributes significantly to the degradability characteristics of the resultant films or coatings.
The polyesters of the present invention are generally not soluble in water. This allows the materials of the present invention to advantageously have greater dimensional stability in the presence of moisture. This is contrasted to the sulfo-containing copolyesters of the art which incorporate higher levels (e.g., greater than 5 mole percent) of sulfo groups.
To give the desired physical properties, the sulfonated aliphatic-aromatic copolyesters of the present invention should have IV equal to or greater than 0.30. Sulfonated aliphatic-aromatic copolyesters which have IV less than 0.30 will tend to be brittle.
Minor amounts (e.g. 0 to about 2 mole percent) of polyfunctional branching agents, such as trimellitic acid or penterythritol residues, may be incorporated to modify the polymer melt or solution rheology, film processing, or the like, if desired.
The polyesters of the present invention may be prepared by any desired polycondensation techniques. For example, the various monomeric components can be charged to a polymerization vessel along with polymerization catalysts, for example, manganese and antimony catalyst, and subjected to polycondensation conditions to produce a linear polyester in which the units are randomly distributed along the molecular chain. It will be understood that it is useful, however, to first react two or more of the monomeric components to a prepolymer stage, followed by addition of the remaining components, which may be polymeric, and completion of the polymerization.
The sulfonated, aliphatic-aromatic copolyesters have been surprisingly found to be both biodegradable and solvent soluble in common, non-halogenated, polar solvents. Such solubility advantageously allows for the solvent casting of coating and films from the instant copolyester. Examples of the non-halogenated, polar solvents include tetrahydrofuran, dimethyl acetamide, dimethyl formamide, N-methylpyrollidone, dimethylsulfoxide, and the like. Tetrahydrofuran is a preferred solvent for solvent casting. The copolyesters have been found to be readily soluble in said solvents and the resulting polymer solutions have been found to provide clear films.
The copolyesters of the present invention can be used with additives known within the art. Such additives include thermal stabilizers, for example, phenolic antioxidants, secondary thermal stabilizers, for example, thioethers and phosphites, UV absorbers, for example benzophenone- and benzotriazole-derivatives, UV stabilizers, for example, hindered amine light stabilizers, (HALS), and the like. The additives may further include plasticizers, processing aides, lubricants, and the like. In addition, the compositions of the present invention may be filled with, for example, wood flour, gypsum, wollastonite, chalk, kaolin, cellulose, starch, calcium carbonate, and the like. The compositions of the present invention may also find use as a component of a polymer blend with other polymers, such as cellulose ethers, thermoplastic starch and the like.
As a further aspect of the present invention, the copolyesters have been found to be useful within a wide variety of shaped biodegradable articles. The copolyesters may be solution or melt processed to form coatings, films, and the like. Coatings may be produced, e.g., by coating a substrate with polymer solutions of the copolyesters followed by drying, by coextruding the copolyesters with other materials, or by melt coating a preformed substrate with the polyesters. The copolyesters will find utility in any process incorporating polyester known within the art. Coatings derived from the copolyesters will find utility as barriers to moisture, oxygen, carbon dioxide and the like. The coatings derived from the copolyesters will also be useful as adhesives. Films of the copolyesters may be produced by any known art method, including, for example, solution or melt casting.
The following examples illustrate, but do no limit the invention.